The ability to separate a particle/fluid mixture into its separate components is desirable in many applications. Acoustophoresis is the separation of particles using high intensity sound waves, and without the use of membranes or physical size exclusion filters. It has been known that high intensity standing waves of sound can exert forces on particles in a fluid when there is a differential in both density and/or compressibility, otherwise known as the acoustic contrast factor. The pressure profile in a standing wave contains areas of local minimum pressure amplitudes at its nodes and local maxima at its anti-nodes. Depending on the density and compressibility of the particles, they will be trapped at the nodes or anti-nodes of the standing wave. The higher the frequency of the standing wave, the smaller the particles that can be trapped due the pressure of the standing wave.
Growth in the field of biotechnology has been due to many factors, some of which include the improvements in the equipment available for bioreactors. Improvements in equipment have allowed for larger volumes and lower cost for the production of biologically derived materials such as monoclonal antibodies and recombinant proteins. One of the key components used in the manufacturing processes of new biologically based pharmaceuticals is the bioreactor and the ancillary processes associated therewith.
A modern bioreactor is a very complicated piece of equipment. It provides for, among other parameters, the regulation of fluid flow rates, gas content, temperature, pH and oxygen content. All of these parameters can be tuned to allow the cell culture to be as efficient as possible of producing the desired biomolecules from the bioreactor process. One process for using a bioreactor is the perfusion process. The perfusion process is distinguished from the batch and fed-batch processes by its lower capital cost and higher throughput.
In the fed-batch process, a culture is seeded in a bioreactor. The gradual addition of a fresh volume of selected nutrients during the growth cycle is used to improve productivity and growth. The product, typically a monoclonal antibody or a recombinant protein, is recovered after the culture is harvested. Separating the cells, cell debris and other waste products from the desired product is currently performed using various types of filters for separation. Such filters are expensive and become clogged and non-functional as the bioreactor material is processed. A fed-batch bioreactor also has high start-up costs, and generally requires a large volume to obtain a cost-effective amount of product at the end of the growth cycle, and such processes include large amounts of non-productive downtime.
A perfusion bioreactor processes a continuous supply of fresh media that is fed into the bioreactor while growth-inhibiting byproducts are constantly removed. The nonproductive downtime can be reduced or eliminated with a perfusion bioreactor process. The cell densities achieved in perfusion culture (30-100 million cells/mL) are typically higher than for fed-batch modes (5-25 million cells/mL). However, a perfusion bioreactor requires a cell retention device to prevent escape of the culture when byproducts are being removed. These cell retention systems add a level of complexity to the perfusion process, requiring management, control, and maintenance for successful operation. Operational issues such as malfunction or failure of the cell retention equipment has previously been a problem with perfusion bioreactors. This has limited their attractiveness in the past.
It would be desirable to provide means that can reduce the cost and effort of using bioreactors and separating the desired products from the cells that make them.